Method for metallizing non-conductive substrates

ABSTRACT

A method comprising the steps of (a) preparing a divided copper oxide dispersion (4) including a solvent and a selected binder, (b) applying said dispersion to a non-conductive substrate (1) to form a film (5), (c) forming a Cu film (9) with a suitable reagent, and (d) electrolytically depositing at least one metal film (11) on said film (9).

This is a national stage application of PCT/FR94100860 filed Jul. 11,1994

FIELD OF THE INVENTION

The invention relates to a process for metallizing nonconductivesubstrates.

PRIOR ART

Numerous processes are already known for forming a metallic layer on anonconductive substrate or support, whether this pertains to glass,plastic materials, composite materials with a nonconductive matrix,paper, ceramic materials, etc.

A first family of processes calls for the deposition by evaporationunder vacuum of liquid metal thanks to various means of heating (Jouleeffect, electron bombardment, cathode sputtering, etc.). Thus, it ispossible to deposit a layer of aluminum on films typically made ofplastic material (PET, for example).

As variants of these processes, one finds the processes of depositionchemically known under the term "CVD" (chemical vapor deposition),possibly with the help of a plasma (PEVD processes=Plasma Enhanced VaporDeposition).

The processes of chemical or electrochemical deposition of metals arealso known.

These processes are considered conventional in the case of conductivesupports.

In the case of nonconductive supports, a preliminary treatment isnecessary before proceeding with the actual chemical or electrochemicaldeposition.

This treatment can be metallization under vacuum, as described in thepatent FR-A1-2 558 485 relating to the manufacturing of a porousmetallic structure.

This treatment can also be an activation treatment based on preciousmetals (silver, palladium, gold), as described in the work"Electroplating of Plastics--J. Christof et al.--Finishing PublicationsLtd. 1977 UK," or else in the work "Surface Finishing Systems: Metal andNonmetal Finishing Handbook-Guide--by George J. Rudzki--FinishingPublications Ltd. 1983--England."

The typical process includes the sequence of the following steps:

etching of the substrate with chromic acid;

treatment with a stannous chloride solution;

treatment with a solution containing a precious metal such as Ag, Pd,Au;

immersion in a bath called "electroless" (chemical deposition, orautocatalytic deposition!) allowing one to deposit metals such assilver, copper, nickel, or tin (relatively slow deposition);

finally, electrolytic covering with the metal to be deposited (much morerapid deposition than the chemical deposition--necessary step forobtaining a conductive surface). Finally, there are processes in whichthe preliminary treatment, necessary for the implementation ofconventional chemical or electrochemical depositions (respectively,reduction of a metallic salt chemically, using a reducing agent, orelectrochemically), consists of incorporating in the substrateconductive fillers such as conductive flakes or powders (metallicpowders, fibers of carbon, graphite, etc.), or fillers made conductiveby reduction.

Thus, French application FR-A-2 544 340 describes a process formanufacturing a conductive film which includes the following steps:

one forms a collodion of a heat-hardening resin containing 20 to 60 wt %Cu₂ O in powder form;

one forms a film from this collodion;

one draws the film or mechanically pickles it in order to expose on thesurface (bring to light) particles of Cu₂ O;

one reduces the particles of Cu₂ O on the surface by borohydride;

then, one carries out an electrolytic deposition.

Likewise, in the French application FR-A-2 518 126, a process isdescribed for metallizing a molded object by electrolytic deposition,which includes the following steps (Example 1).

formation of a mixture of prepolymer material and Cu₂ O powder;

molding of the mixture in order to obtain said object and crosslinkingof the prepolymer material;

treatment of the surfaces of said object with a gentle abrasive, dustremoval, and treatment in an ultrasound tank, in order to expose theparticles of Cu₂ O;

formation of copper by reduction of Cu₂ O with borohydride;

then, electrolytic deposition of copper.

There are also known processes which allow one to carry out anelectroless metallic deposition without the need for an activationtreatment using a precious metal.

Thus, U.S. Pat. Nos. 3,146,125 and 3,226,256 disclose processes whichtypically include the following steps:

preparation of a mixture of prepolymer and Cu₂ O powder;

molding of this mixture, or application of this mixture in the manner ofan ink on an insulating support;

crosslinking of this mixture;

possible abrasion of the surface in order to expose the Cu₂ O particles;

dismutation of Cu₂ O by sulfuric acid;

then, electroless metallic deposition.

Finally, there are known processes, as described in U.S. Pat. No.4,327,125, in which one deposits on the nonconductive surface to becopper-plated a colloid of Cu particles, formed from a copper salt and areducing agent; then, one performs a chemical deposition of copper in anelectroless bath.

Purposes of the Invention

The purpose of the invention is a treatment of any nonconductivesurface, of any shape, allowing one then to carry out a metallization,not only by electroless deposition, but above all by electrolyticdeposition, which is advantageous from an economic standpoint, given thehigh rate of deposition of the electrolytic method.

DESCRIPTION OF THE INVENTION

The invention can be implemented according to two practical modes.

According to a first mode of the invention, the process formanufacturing a continuous metallic deposit on a nonconductive substrateincludes the following steps:

a) one prepares a dispersion of copper oxide in the divided state, whichis capable of being transformed, at least in part, to the state ofmetallic copper by the action of a reagent, which contains a solvent anda binder selected to form, after elimination of the solvent, a film thatis permeable to said reagent;

b) one applies said dispersion on said nonconductive substrate, and oneforms a thin layer on said nonconductive substrate which contains saidcopper oxide in the divided state, with a thickness of less than 30 μm;

c) one forms Cu from said copper oxide by the action of said reagent, soas to obtain, on the surface of the nonconductive substrate, a thinlayer containing Cu;

d) one deposits, on said layer containing Cu, at least one metalliclayer by electrolytic deposition of at least one ionic metallic speciesin solution.

Thus in comparison with prior art, the invention constitutes a simplerand more economical process: it is sufficient, on the one hand, toproduce a dispersion of copper oxide, which is obtained from commercialproducts, and to apply, with no special means, as a paint, an ink or avarnish, on any nonconductive substrate, which is most often, but notnecessarily, in its final form, and on the other hand, to transform allor part of this oxide into Cu, in a manner known in itself, beforeproducing a metallic deposit by electrolytic deposition.

Certainly, the use of Cu₂ O was already known in metallizing treatmentsof prior art for the purpose of allowing for subsequent electrolyticdeposition, but under completely different conditions, since in theapplication FR-A-2 518 126, the Cu₂ O is not deposited on the surfacebut intimately bound with the nonconductive substrate itself, the latterbeing molded in the presence of Cu₂ O. The surface of the molded objectobtained is then abraded in order to allow for the action of aborohydride as agent for reducing Cu₂ O, in such a way as to obtain ahigh degree of electrical conductivity.

Such a process would therefore not be applicable, according to theinvention, to any substrate such as a porous foam, with an interiorsurface of the pores which is inaccessible to abrasive action.

The present invention offers a particularly surprising characteristicinsofar as in spite of the fact that by steps a) to c), one forms a thinlayer containing little copper and which is therefore not veryconductive, it is possible according to the invention then to form ametallic layer by electrolytic deposition.

Whereas the surface resistivity obtained after the treatment describedin the French application FR 2 518 126 is between 0.01 and 1000Ω/square, that obtained after steps a) to c) according to the presentinvention is at a much higher level which can reach 20×10⁶ Ω/square or aresistivity that is 20,000 times higher than that indicated in theapplication FR 2 518 126.

Furthermore, the studies undertaken by the applicant have shown that thepossibilities for performing a metal deposition electrolytically are notcorrelated with this criterion of resistivity, contrary to what thestudy of prior art could allow one to assume. See Example 3.

In contrast, these studies have shown that the nature and the state ofthe binder (crosslinked or not) play a decisive part, as illustrated inExamples 5 and 6.

DESCRIPTION OF THE FIGURES

All the figures relate to the invention.

FIGS. 1 to 3 illustrate the different steps of the process according todifferent variants relating either to the nature of nonconductivesubstrate (1) (material with apparent porosity in FIG. 1; cellularmaterial with apparent porosity in FIG. 2), or to the nature of thedispersion applied on this substrate (1) (dispersion (4) containing Cu₂O powder in FIGS. 1 and 2; dispersion (4a) containing a conductivepowder in FIG. 3).

In the process represented in FIG. 1, substrate (1) is coated on onesurface with dispersion (4), in a solvent medium, of Cu₂ O powder(represented by small circles) and binder according to the invention, insuch a way as to obtain, after elimination of said solvent by drying,multilayer material (20) formed by support (1) covered with thin layer(5a) containing Cu₂ O and the binder according to the invention. Afterimmersion in an acid solution, one obtains multilayer material (21)formed by support (1) covered with thin layer (9) containing conductiveparticles (Cu) (represented by crosses). After electrolytic depositionof metal in electrolysis bath (10), provided with cathode (15) and anode(16), one obtains multilayer material (22) which has metallic layer (11)with the desired thickness.

This multilayer material can then also be transformed, either byseparating the substrate in such a way as to obtain essentially metallicmaterial (23), or by heat-treating material (22) in such a way as toobtain material (24) by crosslinking said binder and thus solidlyconnecting said substrate (1) and said metallic layer (11).

In FIG. 2, which differs from FIG. 1 by the nature of the substrate, theprocess of the invention has been applied to foam (1a) with apparentporosity (diagrammed by the representation of a pore in cross section).By immersion of the foam in dispersion (4) and then removal and drying,one obtains material (20a) in which the whole surface of the pores iscovered with layer (5a) which contains Cu₂ O and the binder according tothe invention.

By acid treatment, one forms material (21a) in which the surface of thepores is covered with layer (9) containing conductive particles (Cu) andsaid binder. Then, by electrolytic deposition, one obtains material(22a) of which the whole surface of the pores is covered with metalliclayer (11).

In FIG. 3, similar to FIG. 1, dispersion (4a) contains conductiveparticles, instead of containing Cu₂ O as in dispersion (4) of FIG. 1.After application of a thin film of this dispersion and drying, oneobtains materials (21) which have layer (9a) of conductive particles insaid binder.

FIG. 4 represents the electrical assembly allowing one to determine thesurface resistivity of materials (9,9a).

This resistivity (Ω/square) is given by the formula: (3.14×ΔV/I×1n2),the measuring electrodes being 25 mm apart.

FIGS. 5, 5a, and 6 illustrate in cross section a preferred manner offorming metallic layer (11) by electrolysis, in bath (10), the transportof the current being ensured by cathode (15) and anode (16):

One first forms "primary" metallic film (14) by growth of the metallicfilm from the point of electrical contact with layer (9), so as to coverprogressively the whole surface of layer (9).

FIG. 5a represents a front view in which metallic film (14) coversapproximately half the surface of layer (9) and progresses towards thebottom in the direction of the arrow, the point of electrical contactwith layer (9) having been placed at the upper end of layer (9).

Then, once the metallic film is formed over the whole surface S of layer(9), the electrolysis is carried out in order to increase the thicknessof metallic film (14) and to obtain metallic layer (11).

FIG. 6 diagrams in a graph J=f(t) in which J, on the y axis, representsthe intensity of the current in A, the surface area in this case being 1dm², and in which t, on the x axis, represents the time in min of thetwo electrolysis steps:

The first step, whose duration is noted Δt_(s), aims to progressivelycover the whole surface S of layer (9) with metallic film (14) withthickness Ei, which takes place with a progressive increase of thecurrent density.

The second step, whose total duration is noted Δt_(e), aims to increasethe thickness of the metallic layer, which goes from the initialthickness E_(i) to the thickness E_(f) in final metallic layer (11).

FIG. 7 represents, in cross section, the diagram of an electrolyticdeposition installation for implementation of a mode of the inventionaiming to continuously produce metallic strip (13). This diagram makesit possible to illustrate the process according to one mode of theinvention.

Substrate (1) is a plastic film in wound form (represented by a striphatched laterally).

The installation successively includes:

means (2) of supplying substrate (1);

means (3) for applying on substrate (1), thin layer (5) (represented bycircles) of dispersion (4) of Cu₂ O in a solvent;

means (6) of drying said thin layer (5);

means (7) of washing said thin layer (5) with acid and means of rinsing(8) with water, leading to the formation of said thin layer (9) whichcontains Cu (represented by crosses);

means ensuring the electrolytic deposition of metallic layer (11) in twosuccessive baths:

In the first (10a), the metallic salt concentration and the electricalparameters, current voltage between cathode (15) and anode (16a) andintensity, are chosen so as to obtain, leaving the bath, a metallic filmwith a thickness E_(i) of a few μm.

In second bath (10), the intensity of the current running throughcathode (15) and anode (16) is greater than that in the first bath, andit is suitable for the rapid formation of metallic layer (11) with thedesired thickness E_(f).

Leaving the electrolysis bath, the plastic strip serving as support (1)is separated from metallic strip (13). The plastic strip is possiblyreintroduced at the top of the device, thanks to guiding means (12).

DETAILED DESCRIPTION OF THE INVENTION

For the implementation of the first mode of the invention, it ispossible to choose, as copper oxide, either CuO or Cu₂ O, said reagentbeing a reducing agent in the case of CuO, and said reagent being eithera reducing agent or a dismutation agent in the case of Cu₂ O.

Said dispersion (4) of CuO or Cu₂ O in a solvent, prepared in step a) ofthe process, contains a fine dispersion of CuO or Cu₂ O in the form ofparticles whose average size is less than 30 μm, preferably less than 10μm, and greater than 0.1 μm.

The CuO or Cu₂ O content in said dispersion (4) is between 20 and 80%.

If one wishes to obtain a fluid dispersion, the Cu₂ O or CuO content insaid dispersion will generally be between 20 and 60 wt %, but in otherrespects, the viscosity, which increases with the Cu₂ O or CuO content,also depends on the other constituents of the dispersion.

The formation of Cu from Cu₂ O can be brought about according to twoconventional methods, by action of a reducing agent or by dismutation.

The dismutation (disproportionation in English) of Cu₂ O is in itself aknown reaction which can be written (balanced reaction):

    2 Cu.sup.+ <-->Cu.sup.++ +Cu

It is advantageous according to the invention to choose the reaction ofCu₂ O dismutation and preferably to choose, as reagent, a dismutationagent which is an acid for the following reasons:

on one hand, the action of an acid on said thin layer containing Cu₂ Ois more rapid than that of a reducing agent: the mobility (the ease ofpenetration into said layer) of the H⁺ ions is much greater than that ofa reducing agent such as a borohydride. Hence, the possibility forcontinuous treatment.

on the other hand, according to a hypothesis of the applicant, it ispossible that the penetration of the acid into said thin layercontaining Cu₂ O and the dismutation reaction itself leads, by formationof a Cu⁺⁺ ion which is soluble in aqueous medium, to a porosity in saidthin layer containing Cu which greatly improves the electrolytic contactbetween the metallic Cu deposit of said thin layer containing Cu and thewhole metallic ion solution to be deposited.

finally, ordinary acids are much more economical than the reducingagents such as the borohydrides.

Furthermore, in should be emphasized that, as demonstrated aftermeasurements of surface resistivity done in the context of the researchof the applicant, a surface with a low resistivity no longer seems to bea necessity for being able to carry out subsequently and directly anelectrolytic deposition. According to the invention, it is not necessaryto attempt to increase the quantity of conductive particles, since asurface resistivity, which can be as high as 40×10⁶ Ω/square issufficient to obtain the primary technical effect which allows forsubsequent electrolytic deposition.

In the case of dismutation of Cu₂ O using acid, one preferably operateswith a dilute acid in aqueous solution.

Said acid is chosen from the group formed by acetic, formic, nitric,oxalic, phosphoric, sulfamic, sulfuric, and tartaric acids. Sulfuricacid is preferably used.

This dismutation reaction, which leads to the formation of thin layer(9) containing Cu, is generally carried out after drying and eliminationof the volatile materials from thin layer (5). However, it is important,according to the invention, for the drying to be done under conditions,particularly of temperature, which preserve the permeability of thebinder with regard to said reagent. In effect, it is therefore necessaryto avoid drying temperatures which would lead to polymerization orextensive crosslinking of said reagent.

It has been observed, on one hand, that the dismutation reaction is veryrapid, on the order of a few seconds, typically 5 to 20 sec, and on theother hand, that the thin layers, layers (5a) and then (9), keep theirintegrity and do not disintegrate during the drying, during the phase ofwashing with acid and of rinsing with water, which is essential for theimplementation of the invention. These are two essential criteria in thechoice of a binder and of the conditions of formation of thin layers(5a) and (9).

According to the invention, it is also possible to carry out thereaction of Cu₂ O with a salt, preferably a water-soluble sulfide (K₂ S,for example). In this case, a black layer forms, on which it is possibleto carry out an electrolytic deposition.

The second practical mode of the invention as already mentioned callsfor the use of conductive particles. In this case, the process accordingto the invention includes the following steps:

a) one prepares dispersion (4a) of an electrically conductive powder, inthe divided state, which contains a solvent and a selected binder;

b) one applies said dispersion (4a) on said nonconductive substrate (1),and one forms thin layer (9a) on said nonconductive substrate whichcontains said conductive powder in the divided state;

c) one deposits on said layer (9a) a metallic layer by electrolyticreduction of at least one ionic metallic species in solution.

But it should be noted that if the use of electrically conductiveparticles is necessary, obtaining of a conductive surface or of asurface with a low resistivity, typically less than 1000 Ω/square, isnot necessary according to the invention in order to be ablesubsequently and directly to carry out an electrolytic deposition; ineffect, a resistivity which can reach 40×10⁶ Ω/square is suitableaccording to the invention, which allows one to use small quantities ofconductive powders or slightly less conductive powders but in a greaterquantity.

Said conductive powder is preferably a graphite powder with a particlesize of less than 50 μm, but any conductive powder, such as a metallicpowder, for example, could be suitable, provided that a metal that isnot very oxidizable is chosen.

Preferably, said graphite powder is in the form of flakes 1 to 3 μmthick and in which the largest dimension is 5 to 20 μm.

Regardless of the mode of implementation of the invention, said fluiddispersion (4,4a) can be applied on said nonconductive substrate (1) bycoating, dipping, slip painting, spraying or any other method which isknown particularly in the techniques of printing (silk screen process,flexographic printing, etc.) or the techniques of painting, includingindustrial painting, for applying a fluid dispersion in the form of athin layer and with a regular thickness on a substrate, and typicallywith a thickness of less than 30 μm.

Regardless of the mode of the invention, said binder plays roughly thesame part, whether it is a matter of layer (9) containing particles ofCu or of layer (9a) containing conductive particles.

The invention allows one, in step b) of the process, to apply saiddispersion (4) on said nonconductive substrate (1) using a mask,typically by silk screen process, so as to obtain, after step d) of theprocess, conductive metallic tracks, preferably made of copper.

In general, dispersion (4,4a), so that it can be applied on substrate(1), must have sufficient fluidity, which can vary depending on thechosen technique of application. In contrast, once this dispersion isdeposited in a thin layer on the substrate, it is often desirable to setthis dispersion, by any known method for setting a dispersion, andtypically by evaporating said solvent, or by flocculating said binder,or by applying said dispersion with heat (in the fluid state) and thencooling it in order to increase greatly the viscosity, in which caseelimination of the solvent may not be necessary.

The act of setting the dispersion amounts to increasing its cohesion,and most often the adherence of the substrate, which allows for easyhandling of the covered substrate and treatment by said reagent, ifnecessary.

After having formed, directly or not, layer (9,9a) containing conductiveparticles, one proceeds with the electrolytic deposition of metal.

According to the invention, the electrolytic deposition of said metallicspecies is preferably carried out, in one or more electrolysis baths, intwo steps:

in a first step, one produces a "primary" metallic deposit on thesurface treated according to the invention (either after steps a), b)and c) forming layer (9) in the case in which a dispersion (4) of Cu₂ Ois used, or after steps a) and b) forming layer (9a) in the case inwhich dispersion (4a) of conductive powder is used), by growth andpropagation, from at least one point of electrical contact on saidtreated surface, of a metallic film until, by advance of the growthfront of said metallic film, said "primary" metallic film (14) coverssaid treated surface, the thickness of said "primary" metallic film (14)being small and typically less than 10 μm;

in a second step, the thickness E_(i) of said "primary" metallic film isincreased until the desired thickness E_(f) for said metallic layer (11)is obtained.

In said first step, one obtains said "primary" metallic film (14) byprogressively increasing the intensity J or the density I of theelectrolysis current until obtaining a maximum intensity J_(max) (ordensity I_(max)) which typically but not necessarily will be that usedduring said second step, and by limiting the stirring of saidelectrolysis bath. In practice, one multiplies the points of contact inorder to reduce the time of formation (Δt_(s)) of "primary" metallicfilm (14).

Instead of increasing the current density, it is also possible to useincreasing pulsating currents, or also to set the deposition voltage andallow the current to drift, which will then proportionally increase themetallized surface area.

In the case of a progressive increase of the density or intensity(dI_(max) /dt), this is chosen to be as high as possible but below alimit value which can be determined experimentally (dI_(max) /dt)_(max)and beyond which stopping of the growth and of the propagation of saidmetallic film (14) takes place before the whole of said treated surfaceis covered with said metallic film.

In effect, the applicant has observed that an excessive increase of theintensity leads to a sudden stopping of the growth in the surface of themetallic film (14). Detailed examination of the phenomenon has shownthat when the current density is excessive, "burned" deposits form,which is to say that at the growth front of said metallic film, metallichydroxides become incorporated in said film and disturb its growth.

In the case of continuous metallization, two successive electrolysistanks are used, as represented in FIG. 7. Besides the metallic saltconcentration and the suitable choice of the electrical parameters(intensity and voltage), the inclined arrangement of support strip (1)with respect to the metallic tank serving as anode can contribute to theprogressive formation of metallic film (14) in first electrolysis bath(10a) by progressive increase of the electrical field as the stripadvances in bath (10a).

In the case in which bath (10a) has only one point of electrical contactby cathode (15a), the speed of advance of the strip is adjusted based onthe speed of growth and propagation of the metallic film, which istypically at least a few centimeters per min (typically 3 to 4 cm/min).

According to the invention, said binder has a weight content in saiddispersion (4,4a) of less than 20 wt % and is chosen in such a way as:

1) to obtain, as a function of said solvent (binder which must besoluble or able to be finely dispersed in said solvent), stabledispersion (4,4a) of said copper oxide or of said conductive powder;

2) to form continuous thin layer (5,9a) on said substrate, includingafter partial or total elimination of said solvent;

3) to form thin layer (9,9a) which keeps its integrity in anelectrolysis bath.

The first function of the binder is therefore the ability to form a thinand continuous layer covering the particles which does not disintegratein contact with water in particular.

The essential second function which the binder must have is its abilityto allow for the growth of a metallic film under electrolysisconditions. On one hand, it seems to be difficult if not impossible tocorrelate this function with an intrinsic property of the binder, and onthe other hand, as will later be explained in more detail, this abilitydepends also on the surface texture of substrate (1) to be treated. Forall these reasons, said binder is selected based on a test whichincludes steps a) to d) of said process which includes the formation ofthin layer (9) containing particles of copper, in which the parametersother than those relating to the binder and to its solvent arepredetermined:

in step a), one prepares said dispersion (4) which contains, by weight,50% Cu₂ O and roughly 10% of said binder to be tested and 40% of itssolvent;

in step b), one applies said dispersion (4) on a plate of insulatingmaterial (1) to be metallized (10 cm×20 cm×1 cm), a layer (5) 25 μmthick, and one forms thin layer (5a) by eliminating the solvent at atemperature that is sufficiently low not to polymerize or crosslink saidbinder, in the case of a binder that can be thermally polymerized orcrosslinked;

in step c), one treats said plate covered with the dispersion of Cu₂ Ousing 10 wt % sulfuric acid for 1 min in order to bring about thedismutation of Cu₂ O and to form thin layer (9) containing particles ofCu; then one rinses the plate with water;

in step d), one subjects the plate obtained after step c) to a test ofelectrolytic deposition of Cu, under the conditions for formation ofsaid "primary" metallic layer (14) with a current gradient, typically asindicated in FIG. 6 in which Δt_(s) equals 3 min and the currentintensity J is equal to 10 A.

Said binder is selected if, by growth and propagation of a metallicfilm, a "primary" metallic film (14) covering said thin layer (9)progressively forms. See Example 3.

In the case in which the tested material is highly divided (foam withapparent porosity), Δt_(s) should be considerably increased in order toreach, for example, 15 min. See Example 4.

The applicant has observed that all the binders selected using a flatsubstrate (1)0 for example, a plate of plastic material, are notsuitable for a substrate (1) consisting of a foam with apparentporosity, whereas all the binders suitable for a porous substrate arealso suitable for a nonporous substrate.

According to a hypothesis of the applicant, only the most "flexible"binders are suitable for porous substrates, which have internal surfaceswith small radii of curvature or numerous breaks of slopes.

Preferably, said solvent is chosen from the organic solvents, and saidbinder is preferably chosen from the low-molecular oligomers,prepolymers or polymers with polar groups.

It is possible to choose said binder from thermoplastic resins(cellulose acetate buryrates, acrylic, polyamide, polystyrene, vinylisobutyl ether, etc. or resins which can be heat-hardened beforecrosslinking (silicone resins, epoxy resins, phenoxy, polyesters, etc.).

Said binder is preferably chosen from the silicone resins.

These binders can be chosen from the known additives for stabilizingmineral pigments of inks or paints, most often but not exclusively, inan organic solvent medium. These stabilizing agents, of a great chemicalvariety, are molecules, a part of which has an affinity for the productto be dispersed and the other part of which can have an affinity for thesolvent.

These stabilizing agents, which can as well be monomers, oligomers orpolymers with a low to medium molecular weight, can be chosen also as afunction of substrate (1) and the nature of the product which one wishesto manufacture.

In effect, there are cases in which one wishes to manufacture composite(24), "substrate (1)+metallic layer (11) which sticks to the substrate,"and there are cases, as represented in FIG. 7, in which one wishes tomanufacture metallic strip (13,23) and in which, contrary to thepreceding case, one wishes to be able to separate easly said metalliclayer (11) from its substrate (1) in order to obtain metallic strip(13,23).

In the first case, it will be desirable to have an affinity, acompatibility between the chemical nature of the substrate and that ofthe binder so that a certain connection between substrate (1) and layer(5) occurs during the elimination of the solvent and especially during atreatment of crosslinking of said binder subsequent to the deposition ofmetal by electrolysis.

In the second case, on the contrary, chemical incompatibility will bedesirable.

But in all cases, the selected binder must allow for permeability withregard to said reagent and to said electrolysis bath, and in particularrapid migration of the H⁺ ions in the case of the preferred process ofdismutation of Cu₂ O, while keeping its physical integrity in thepresence of said reagent.

The formulation of said dispersion (4) can also call for variousadditives (thickening agents, which can be, for example, of the modifiedcellulose type, aluminosilicates of the montomorillonite type, modifiedBentone®, Thixcin®=castor oil derivative), which are known in themselvesin the field of paints and inks, particularly in order to suit therheological properties of the dispersion to the chosen technique ofapplication, or in order to ensure preservation during the time of saiddispersion. Generally, these additives are used in a small quantity(typically on the order of 1 wt %).

According to the invention, said nonconductive substrate (1) is chosenfrom the group formed by the flat materials (plastic films in woundform, fabrics, nonwoven materials, felts preferably in wound form,etc.), the molded materials (molded parts, tubes, etc.), the cellularmaterials with apparent porosity (foams made of plastic material, feltsmade of textile material, etc.).

There is no limitation of the invention as to the nature and the more orless divided state of said nonconductive substrate (1) (plastic,ceramic, glass, wood, textile, etc.), except that this substrate (1)must not be destroyed during the implementation of the process accordingto the invention, whether this is by the solvent of said dispersion orby the water of said electrolysis bath.

Said substrate (1) can be a material in strip form or in formats sic!and in which the different steps of said manufacturing process can becarried out continuously, as illustrated in FIG. 7 as an example.

After formation of metallic layer (11), the process allows for numerousvariants depending on the nature of the desired final material:

After the step of formation of said metallic layer (11), it is possibleto separate said metallic layer (11) from said nonconductive substrate(1), preferably by physical separation, pyrolysis or chemicaldissolution. One thus obtains essentially metallic material (13,23).

After the step of formation of said metallic layer (11), it is alsopossible not to separate said metallic layer (11) from saidnonconductive substrate (1), and possibly to reinforce the adherencebetween said nonconductive substrate (1) and said metallic layer (11) bypolymerizing or crosslinking said binder after formation of saidmetallic layer (11).

EXAMPLE 1

Using a ball mill, one prepares dispersion (4) with the following weightcomposition:

Cu₂ O: 50%

binder or stabilizing agent: 10%

solvent: 40%

The Cu₂ O is a commercial powder, which after crushing, has an averageparticle size on the order of 2 μm. The binder (stabilizing agent) is acommercial methylphenylsilicone resin, and the solvent istrichloroethylene.

The substrate is a piece of polyurethane foam 10 mm thick, with apparentpores (pores 0.8 to 1 mm).

The substrate was dipped in dispersion (4) and then, after it had beenwithdrawn and drained, it was dried in dry air for one min.

It was then dipped for some ten seconds in a 10% sulfuric acid solutionand then rinsed with water.

This substrate was placed in a conventional electrolysis bath containing80 g/L of CuSO₄, and it was connected to the negative pole of a currentgenerator. This substrate was subjected to electrolysis with a currentdensity I equal to 3 A/dm², for a duration of 20 min, in such a way asto obtain metallic copper film (14) with an average thickness on theorder of 10 μm.

EXAMPLE 2

This example is similar to Example 1, except that the reagent is notsulfuric acid but a 3 wt % potassium sulfide aqueous solution.

One thus obtained a conductive black deposit which allows one to obtaina copper deposit by electrolysis of a copper salt.

EXAMPLE 3

In this example, 11 different binders were tested.

A) Preparation of the dispersions of Cu2^(O) by crushing, as in Example1, of Cu₂ O powder (50 wt % of the dispersion), in trichloroethylene assolvent, in the presence of binder.

The table which follows indicates the nature of the binder and theweight percentage of binder and of solvent in the dispersion.

    ______________________________________                                        Binder                           Solvent                                      Chemical nature/Commercial name                                                                         wt %   wt %                                         ______________________________________                                        1) Polymethylphenylsilicone/NH2246 (R)                                                                  10     40                                           2) Polymethylphenylsilicone/Rhodorsil 1505 (R)                                                          10     40                                           3) Polymethylphenylsilicone/REN50 (R)                                                                   10     40                                           4) Polymethylphenylsilicone/Rhodorsyl 6405                                                              10     40                                           5) Silicone/SR125 (R)     10     40                                           6) Silicone/Dow Corning 808 (R)                                                                         10     40                                           7) Polymethacrylate/Altuglas (R)                                                                        10     40                                           8) Acrylic/Perlucid Re2600 (R)                                                                          10     40                                           9) Epoxide/Duralit R-1516 (R)                                                                           10     40                                           10) Polystyrene (from commercial expanded polystyrene)                                                  1      49                                           11) Cellulose acetate butyrate                                                                          0.8    49.2                                         ______________________________________                                    

The suppliers of these binders are, in the respective order, thecompanies: 1) Hull Sic; possibly, Huls!, 2) Rhone-Poulenc, 3) Wacker, 4)Rhone-Poulenc, 5) G.E. Silicone, 6) Dow Chemical, 7) Altulor, 8) and 9)La Celliose 11) Eastman

B) Application on substrate (1)

The substrate is a Teflon plate with dimensions 143×76×3 (mm).

Each dispersion was applied by immersion in the dispersion,which led tothe formation of wet layer (5) of approximately 30-40 μm.

After drying in air, dry layer (5a) approximately 20 μm thick wasobtained. The 5 lateral layers were eliminated, keeping only the layerwith dimensions 143 mm×76 mm on the substrate.

C) Dismutation of Cu₂ O

The 11 plates were dipped in a 10 wt % sulfuric acid solution, for 1min, and then after rinsing with water, the plates were dried withcompressed air.

D) Measurement of the surface resistivity

For this, the four point measurement illustrated in FIG. 4 was used.

The measurement amounts to measuring the voltage ΔV using a voltmeterand intensity I, while the electrical generator imposes a voltage of 100V.

The values obtained, in Ω/square, are indicated in the table under E).

E) Formation of a copper film (14) by electrolytic deposition asillustrated in FIGS. 5 and 5a.

The electrolysis bath has the composition:

Cu(BF₄)₂ : 450 g/L

HBF₄ : 40 g/L

Electrolysis conditions:

electrical generator=pulsating current generator

temperature of the bath=20°-25° C.

J going from 1 A at the beginning of the electrolysis and reaching 10 Aafter 3 min. Then, a value of 13 A was maintained for 12 min.

In all cases, one observed the formation of metallic film (14) byprogressive propagation and growth of the metallic film from the pointof electrical contact. The speed of propagation was roughly the same forall the binders and close to 50 mm/min. This intermediate metallic film(14) has a thickness on the order of 6 μm.

The table which follows indicates the quantity of copper deposited oneach sample, the theoretical quantity (deposition of copper on a plane)being 3.376 g, and with the surface resistivity opposite this.

    ______________________________________                                                               Cu                                                     Binder                 quantity                                                                              Resistivity                                    Chemical nature/Commercial name                                                                      (g)     10.sup.6 Ω/square                        ______________________________________                                        1) Polymethylphenylsilicone/NH2246 (R)                                                               3.00    21.7                                           2) Polymethylphenylsilicone/Rhodorsil 1505 (R)                                                       2.68    15.5                                           3) Polymethylphenylsilicone/REN50 (R)                                                                2.85    34.5                                           4) Polymethylphenylsilicone/Rhodorsyl 6405                                                           3.06    29                                             5) Silicone/SR125 (R)  2.93    1.7                                            6) Silicone/Dow Corning 808 (R)                                                                      2.95    1.5                                            7) Polymethacrylate/Altuglas (R)                                                                     2.93    2.2                                            8) Acrylic/Perlucid Re2600 (R)                                                                       2.95    23                                             9) Epoxide/Duralit R-1516 (R)                                                                        3.17    39.5                                           10) Polystyrene        2.77    1.1                                            11) Cellulose acetate butyrate                                                                       2.90    8                                              ______________________________________                                    

In conclusion, it is possible to note, on one hand, that there does notseem to be a correlation between the surface resistivity and thequantity of copper deposited, which in all cases, is not far from thetheoretical quantity, which shows that all the binders tested aresuitable for the implementation of the invention in the case of thesubstrate which is used.

EXAMPLE 4

The same series of tests as that of Example 3 was done, but using assubstrate a plate made of polyurethane foam with dimensions 245×55×10mm³.

The only differences with respect to Example 3 are the following:

dismutation of Cu₂ O in 3 min instead of 1 min as in Example 3;

J going from 2 A at the beginning of the electrolysis and reaching 30 Aafter 15 min (Δt_(s)). Then, a value of 35 A was maintained for 15 min(Δt_(E)).

The time (min) necessary for complete covering of the surface (245 mm×55mm), the fraction (%) of the distance travelled by the metallic film(percentage of covering of the surface of the plate), and the weight (g)of copper deposited were measured.

    ______________________________________                                                                      Frac-                                           Binder                 Time   tion   Weight                                   Chemical nature/Commercial name                                                                      (min)  %      (g)                                      ______________________________________                                        1) Polymethylphenylsilicone/NH42246 (R)                                                              15     100    9                                        2) Polymethylphenylsilicone/Rhodorsil 1505 (R)                                                       20     100    7.6                                      3) Polymethylphenylsilicone/REN50 (R)                                                                14.5   100    9                                        4) Polymethylphenylsilicone/Rhodorsyl 6405                                                           17     100    8.6                                      5) Silicone/SR125 (R)  17     100    6.8                                      6) Silicone/Dow Corning 808 (R)                                                                      17     100    3.1                                      7) Polymethacrylate/Altuglas (R)                                                                     --      61    1.3                                      8) Acrylic/Perlucid Re2600 (R)                                                                       --      0     0                                        9) Epoxide/Duralit R-1516 (R)                                                                        --      0     0                                        10) Polystyrene        --      53    5.7                                      11) Cellulose acetate butyrate                                                                       --      32    1.1                                      ______________________________________                                    

In the case of a substrate made of foam with apparent porosity, thistable shows the great selectivity of the test for selecting the binders.

The applicant has issued the hypothesis according to which the lack ofpropagation of the metallic film would be due to the discontinuity ofthin layer (9,9a) containing conductive particles, which discontinuityitself would result from a lesser flexibility of the binder (cracking ofthe layer during drying of the dispersion?).

It should be noted that in the case of a support with apparent porosity,sections based on the final product have shown the continuity ofmetallic film (14) over the whole internal surface of the pores and thenthat of final metallic layer (11).

EXAMPLE 5

A series of tests were run, conducted as in Example 4 and with binder1), but which differ by the electrolysis conditions with variation ofΔt_(s) : J went from 2 A at the beginning of electrolysis reaching 30 Aafter a time Δt_(s). Then, a value of 35 A was maintained for a timeΔt_(E) equal to 30 min.

The following results were obtained, which are expressed by the timenecessary for complete covering of the foam substrate.

    ______________________________________                                                     t.sub.s                                                                              Time for complete                                         TESTS        (min)  covering (min)                                            ______________________________________                                        5a            0     No covering                                               5b            7     Partial covering                                          5c            8      8                                                        5d           10     10                                                        5e           12     12                                                        5f           15     13                                                        5g           20     15                                                        5h           25     16                                                        ______________________________________                                    

For the tests 5c to 5h, the final thickness of metallic layer (11) wasclose to 50 μm.

These tests show clearly that there is a threshold not to be exceededfor the speed of the rise of current density. In the present case, it isnecessary for the speed of the rise to be less than 35 A per 7 min;otherwise, the propagation of the metallic film stops duringelectrolysis or even does not occur at all, as in test 5a.

It should be noted that from the standpoint of productivity, one shouldbe situated just below this threshold (test 5c).

EXAMPLE 6

A series of tests was run, done as in Example 4 and with binder 1), butwhich differ by the degree of crosslinking of the binder:

Test 6a=test 4-1 in which dispersion (4) containing said binder, afterapplication on substrate (1) in the form of layer (5), is dried in airin order to form material (20) containing layer (5a).

Test 6b=test 6a, except that layer (5) is dried not at approximatelyroom temperature, but at 130° C. for 4 h.

Test 6c=test 6a, except that layer (5) is dried at 200° C. for 30 min.

Results obtained:

Test 6a is equal to test 4-1, and leads to a uniform deposit of metallicform (14) in 15 min, and then to thick metallic layer (11).

In the case of test 6b, only 2/3 of the foam plate was covered with ametallic deposit, even after 1 h of electrolysis.

In test 6c, no metallic deposit formed even after 1 hour ofelectrolysis.

These tests confirm the decisive significance of the absence ofcrosslinking of the binder.

EXAMPLE 7

In test 7a, the conditions of test 6c were reproduced, except that thechosen substrate was a glass plate (120 mm×60 mm×2 mm) instead of beinga polyurethane foam plate.

In test 7b, the conditions of test 7a were reproduced, except that aftercooking at 200° C., the surface of layer (5a) was abraded before theplate was treated with dilute sulfuric acid in order to bring aboutdismutation of the Cu₂ O powder.

Results:

In test 7a, as in test 6c, no copper deposit forms by electrolysis.

In test 7b, metallic film (14) forms covering the whole of the plateover 120 mm in 8 min (Δt_(s)).

These tests confirm the results of the tests of Example 6 and show thatit is essential for the binder, by its chemical nature and/or its moreor less crosslinked state, not to be capable of withdrawing theparticles of Cu₂ O from the dismutation action of the sulfuric acid.

Other tests conducted with conductive powders ended with the sameconclusions, namely the need to obtain layer (9,9a) containingconductive particles not isolated from the electrolysis bath.

Additional Purposes of the Invention

The invention has, as additional purposes the various products which theprocess according to the invention allows one to obtain.

These products can be of three types:

a) material (22a) consisting of the combination of insulating substrate(1) and metallic film (14) with a small thickness, typically less than10 μm,

b) composite material (24) consisting of the close combination ofinsulating substrate (1) and metallic layer (11) with a thicknessgreater than 10 μm, with it possible for the substrate to be anysubstrate (plastic film, porous foam, fabric, glass, etc.),

c) material (23) essentially consisting of metallic layer (11).

In each of these types of products, metallic layer (11) can includemetallic layers of different metals.

Applications of the Invention

The invention has numerous applications, among which it is possible tomention:

the manufacture of thin metallic sheets (sheets of nickel, copper,nickel/copper, etc.);

the manufacturing of supports for catalysts which require a high surfacearea:volume ratio, by starting, as in Example 4, with a substrate withapparent porosity which itself has a high surface area/volume ratio, andby possibly eliminating the initial substrate after deposition of themetallic layer;

the manufacture of conductive tracks (Cu preferably) which stick to aninsulating substrate for instrumentation, for example, for themanufacture of force sensors;

the manufacture of porous structures (with Cu preferably) used for heatexchangers;

the manufacture of porous metallic electrodes for storage batteries, orthe manufacture of supports for storage battery electrodes, which can becovered with metals such as cadmium, nickel, copper, etc.;

interference elimination for rigid or flexible nonconductive substrates,

antistatic treatment of rigid or flexible nonconductive substrates(including fabrics).

Advantages of the Invention

As already demonstrated, the invention solves numerous problemsencountered with the processes of prior art, since the process accordingto the invention:

a) can be applied, with no known limitations, to any type of support,the treatment according to the invention in a way amounting to applyinga "paint" on any insulating substrate (massive object, film, foam,fabrics, etc.);

b) is very flexible, because of the possibility for obtaining a widerange of final products, by combinations of various substrates andmetallic layers using roughly the same production tools.

c) is economical in terms of consumable material and in terms ofmanufacturing costs, allowing for any electrolytic deposition withoutcalling for costly reagents or special treatment steps.

d) is economical in terms of investment, the depositions being carriedout by traditional means (without the need for techniques under vacuumand/or at high temperature).

e) is very productive, because of the possibility for forming anelectrolytic deposit on a very wide substrate (1 to 2 m) continuously.

We claim:
 1. A process for manufacturing a continuous metallic depositon a non-conducting substrate, comprising:applying a dispersion on anon-conductive substrate, to form a layer, wherein said dispersioncomprises copper oxide, a solvent and a binder; forming copper from atleast part of said copper oxide with a reagent; and depositing on saidlayer at least one metallic layer by electrolytic deposition in anelectrolysis bath; wherein said binder is selected so that a film ofsaid binder is permeable to said reagent, and said binder is selectedfrom binders that allow progressive formation by electrolytic depositionfrom a point of electrical contact of a metallic film covering all of atest layer, wherein said test layer is formed by a process comprising(i)applying, on a plate of insulating material 10 cm×20 cm×1 cm, a 25 μmthick layer of a test dispersion comprising, by weight, 50% Cu₂ O, 10%of said binder and 40% of a test solvent, (ii) eliminating said testsolvent at a temperature which is sufficiently low so as not topolymerize or crosslink said binder; (iii) treating said plate with 10wt % sulfuric acid for one minute in order to dismutate Cu₂ O, and thenrinsing said plate with water, to form said test layer.
 2. A processaccording to claim 1 in which said copper oxide is either CuO or Cu₂ O,said reagent being a reducing agent in the case of CuO, and said reagentbeing either a reducing agent or a dismutation agent in the case of Cu₂O.
 3. A process according to claim 2 in which said dispersion comprisesa fine dispersion of CuO or Cu₂ O in the form of particles whose averagesize is less than 30 μm.
 4. A process according to claim 3 in which theCuO or Cu₂ O content in said dispersion is between 20 and 80 wt %.
 5. Aprocess according to claim 4 in which, said copper oxide is Cu₂ O andsaid reagent is said dismutation agent.
 6. A process according to claim5 in which said dismutating agent is selected from the group consistingof acetic, formic, nitric, oxalic, phosphoric, sulfamic, sulfuric, andtartaric acids.
 7. A process according to claim 6 in which Cu₂ O isreacted with a salt.
 8. A process according to claim 1 in which saidsolvent is an organic solvents, and said binder is chosen fromlow-molecular oligomers, prepolymers or polymers with polar groups.
 9. Aprocess according to claim 8 in which said binder is chosen fromthermoplastic resins or resins which can be heat-hardened beforecrosslinking.
 10. A process according to claim 9 in which said binder isselected from silicone resins.
 11. A process according to claim 1 inwhich said nonconductive substrate is chosen from the group consistingof flat materials molded materials or cellular materials with apparentporosity.
 12. A process according to claim 11 in which said substrate isa material in strip form or in formats and in which the steps of saidprocess are performed continuously.
 13. A process according to claim 1further comprising, after the step of forming said metallic layer,separating said metallic layer from said nonconductive substrate.
 14. Aprocess according to claim 1 in which, after the step of formation ofsaid metallic layer said metallic layer is not separated from saidnonconductive substrate.
 15. A process according to claim 1, whereinsaid layer has a thickness of less than 30 μm.
 16. A process accordingto claim 15, wherein said applying is carried out with a mask so as toobtain after said depositing conductive metallic tracks.
 17. A processaccording to claim 15, further comprising, after said applying, settingsaid layer by: (a) evaporating said solvent, (b) flocculating saidbinder, or (c) heating and cooling.
 18. A process according to claim 17,wherein said depositing is carried out in two steps comprising:producinga primary metallic deposit by growth and propagation of a metallic filmfrom at least one point of electrical contact of an electrode and saidlayer, to form said primary metallic deposit with a thickness of lessthan 10 μm; and increasing the thickness of said primary metallic film.19. A process according to claim 18 in which, in a first step, obtainingsaid primary metallic film by progressively increasing an intensity ofan electrolysis current until obtaining a maximum intensity I_(max), andlimiting the stirring of said electrolysis bath.
 20. A process accordingto claim 19 in which a progressive increase of intensity (dI_(max) /dt)is chosen to be below a limit value beyond which stopping of the growthand of the propagation of said metallic film takes place before thewhole of said treated surface is covered with said metallic film.
 21. Aprocess according to claim 20 in which said binder has a weight contentin said dispersion of less than 20 wt % and is chosen in such a wayas 1) to obtain a stable dispersion of said copper oxide 2) to form acontinuous thin layer on said substrate, including after partial ortotal elimination of said solvent, and 3) to keep said thin layer'sintegrity in said electrolysis bath.
 22. A process for manufacturing acontinuous metallic deposit on a non-conductive substrate,comprising:applying a dispersion on a non-conductive substrate, to forma layer, wherein said dispersion comprises an electrically conductivepowder, a solvent and a binder; and depositing on said layer a metalliclayer by electrolytic reduction of at least one ionic metallic speciesfrom solution; wherein said binder is selected from binders that allowprogressive formation by electrolytic deposition from a point ofelectrical contact of a metallic film covering all of a test layer,wherein said test layer is formed by a process comprising(i) applying,on a plate of insulating material 10 cm×20 cm×1 cm, a 25 μm thick layerof a test dispersion comprising, by weight, 50% Cu₂ O, 10% of saidbinder and 40% of a test solvent, (ii) eliminating said test solvent ata temperature which is sufficiently low so as not to polymerize orcrosslink said binder; (iii) treating said plate with 10 wt % sulfuricacid for one minute in order to dismutate Cu₂ O, and then rinsing saidplate with water, to form said test layer.
 23. A process according toclaim 22 in which said conductive powder is a graphite powder with aparticle size of less than 50 μm.
 24. A process for manufacturing acontinuous metallic deposit on a non-conductive substrate,comprising:applying a dispersion on a non-conductive substrate, to forma layer, wherein said dispersion comprises copper oxide, a solvent and abinder; forming copper from at least a portion of said copper oxide witha reagent; and depositing on said layer, without removing said binder,at least one metallic layer by electrolytic deposition; wherein saidbinder is selected so that a film of said binder is permeable to saidreagent.
 25. A process for manufacturing a continuous metallic depositon a non-conductive substrate, comprising:applying a dispersion on anon-conductive substrate, to form a layer, wherein said dispersioncomprises an electrically conductive powder, a solvent and a binder; anddepositing on said layer, without removing said binder, a metallic layerby electrolytic reduction of at least one ionic metallic species fromsolution.
 26. A process according to claim 25, wherein said layer has aresistivity of at least 1.1×10⁶ Ω/square.